In this work, the high-temperature behavior of nanocrystalline
TiO2 is studied using in situ transmission electron microscopy
(TEM). These nanoparticles are made using wet chemical techniques that
generate the anatase phase of TiO2 with average grain sizes of
6 nm. X-ray diffraction studies of nanophase TiO2 indicate the
material undergoes a solid-solid phase transformation to the stable rutile
phase between 600° and 900°C. This phase transition is not
observed in the TEM samples, which remain anatase up to temperatures as
high as 1000°C. Above 1000°C, nanoparticles become mobile on the
amorphous carbon grid and by 1300°C, all anatase diffraction is lost
and larger (50 nm) single crystals of a new phase are present. This new
phase is identified as TiC both from high-resolution electron microscopy
after heat treatment and electron diffraction collected during in situ
heating experiments. Video images of the particle motion in situ show the
nanoparticles diffusing and interacting with the underlying grid material
as the reaction from TiO2 to TiC proceeds.
In-situ Observation of Phase Transition in Ca-poor Pyroxenes using High Temperature Transmission Electron Microscopy.
